This invention relates to the preparation of pre-cooked food products and more particularly to a process and apparatus for preparing pre-cooked meat products which may be stored and subsequently may be quickly heated prior to serving.
In the commercial processing of foods for distribution to consumers, considerable emphasis is currently being directed to reducing the time and effort needed to prepare the food for serving. While some foods are naturally adapted to serving with a minimum of time and effort, others have characteristics which seemingly require prolonged cooking and which are incompatible with pre-cooking by conventional techniques. Bacon and other fatty meats, such as sausage and spareribs, are examples of foods which long resisted attempts to develop a practical commercial pre-cooking process.
The cooking of bacon, for example, is a process in which fat is rendered, water is evaporated and protein is cooked and this has required an inconvenient amount of time if performed just prior to consumption. It has been difficult to develop a practical technique for pre-cooking bacon inasmuch as the product, if prepared by conventional methods, is either expensive to produce, too oily, low in saleable yield or difficult to control in uniformity of cook. Bacon produced in a continuous oil fryer is oil soaked and tends to be twisted up. Bacon produced in a continuous infra-red oven cooks unevenly with a high rejection rate and causes equipment contamination problems.
Many other meat products have not been readily susceptible to pre-cooking by conventional techniques prior to distribution. Jerky-like products, for example, need little or no preparation immediately prior to consumption, but have conventionally required very extensive or prolonged pre-treatment.
The recent development of microwave heating in the presence of a hot air flow has provided a highly significant advance in the art of pre-cooking meat products. The unique nature of microwave heating, in which the product is heated uniformly throughout rather than being cooked progressively from the exterior surfaces inward, not only greatly shortens cooking time but in many cases also imparts desirable properties to the finished product. U.S. Pat. No. 3,321,314, for example, discloses a process for pre-cooking bacon with microwave energy accompanied by a hot air flow which not only reduces cooking time but also provides good end point control so the bacon is neither overcooked and brittle or undercooked and greasy. Bulk handling and distribution is practical. Microwave heating in the presence of hot air has also been applied to many other meat products with equally beneficial results.
An important consideration in adapting microwave heating to food processing, and particularly to the treatment of foods which require a sizeable heat input, is that of minimizing the microwave input required to accomplish the desired result. Microwave is a relatively costly heating technique. The magnetron tubes or the like used for generating microwave frequencies, and the necessary waveguides and other auxiliary equipment, are costly items. Electrical power consumption is high relative to the actual heat input to the product as a sizeable portion of the energy is ultimately dissipated by heating components of the processing apparatus rather than the product itself. Where the products are handled on a high volume basis, the physical size of a conveyorized microwave tunnel may also create problems.
Microwave energy does not couple strongly to cold fats but strongly heats moisture present in or on a product. Microwave also tends to cause moisture migration to the surface of the product and the resulting evaporation maintains the surface region somewhat cooler than the interior. For these and other reasons, optimum results in a microwave heating process often depend on a careful adjustment of process conditions to the characteristics of the particular product at various stages in the course of treatment.